The present invention relates to a rubber tape for making up a rubber component of a tire, an apparatus for making the rubber tape, and a method of manufacturing a tire.
Vehicle tires, especially pneumatic tires are made up of a plurality of rubber components, e.g. tread rubber, sidewall rubber, clinch rubber, breaker cushion rubber, inner liner rubber and the like.
Usually such rubber components are manufactured by extruding unvulcanized rubber into a specific cross sectional shape which corresponds to the finished shape of the rubber component. This shape is determined by a die of the extruder.
If the rubber component is relatively large, the die becomes large and the size of the extruder can not be reduced. Further, it is necessary to prepare a lot of dies, depending on kinds of the tires to be produced, and the tire sizes, and the number of rubber components. Furthermore, to change the facilities from a certain rubber component to another rubber component, a lot of operations for changing and adjusting the die and the like are necessary.
Therefore, it is impossible to compact the tire production line, and it is difficult to establish a flexible manufacturing system.
On the other hand, in the field of large-sized tires for construction vehicles, as shown in FIG. 10A, it has been proposed to make a tread rubber (e) by winding a rubber strip (a) continuously from one edge to the other edge because it is difficult to extrude a large-sized tire component since a very high extruding pressure is required. This rubber strip (a) has a rectangular cross sectional shape as shown in FIG. 10B.
If this method is employed in making a rubber component for relatively small sized tires such as passenger car tires, the difference of the contour (d) of the wound component from the designed target shape (c) (shown in FIG. 10A by a chain line) becomes large. Further, the surface of the rubber component often corrugates, and lines like clacks are liable to occur on the outer surface of the vulcanized rubber which not only worsens the appearance of the tire but also decreases the strength and durability of the tire if the lines are deep. In particular, when such lines occur on a relatively thin rubber layer such as the sidewall rubber, inner liner rubber and the like, the lines become a weak point.
Further, in comparison with the large-sized tires, small-sized tires need dimensional accuracy in high degree because the tire size is small, and the flow of rubber during vulcanization is limited due to the relatively low tire inflation pressure.
If the size of the rubber tape is decreased, the difference of the contour may be decreased. If the thickness (at) is decreased to less than 0.6 mm, the corrugation on the surface of the rubber component can be neglected, and the occurrence of defective lines may be prevented. In this case, however, the number of windings is greatly increased, and therefore, the working efficiency and production efficiency greatly decrease, and the production cost up is unavoidable. Further, as the rubber tape becomes thin, air becomes liable to remain between the windings of the tape and the total volume of remaining air increases as the number of the windings increases. Thus, separation or cracks are liable to start form the portion where air remains, and it is difficult to improve the tire durability.
Therefore, a primary object of the present invention is to provide a rubber tape which can form a tire rubber component with accuracy without unduly decreasing the thickness and thus can prevent the above-mentioned drawbacks.
Another object of the present invention is to provide a method of manufacturing a tire which can establish a flexible manufacturing system.
Still another object of the present invention is to provide an apparatus for making the rubber tape which is suitably used in the above-mentioned flexible manufacturing system.
According to the present invention, a rubber tape is provided on each side of a central part with a fin, the central part has a thickness of 0.3 to 1.5 mm, and the fin has a thickness less than the thickness of the central part and a width of from 0.5 to 5.0 mm.
According to the present invention, a method of manufacturing a tire comprises a step of making at least one of rubber components by winding the above-mentioned rubber tape.
According to the present invention, an apparatus for making the rubber tape comprises an extruder and a pair of calendar rollers,
the extruder including a die having an extruding hole from which compounded rubber is extruded into a rectangular cross sectional shape, the extruding hole having an opening width WA1 of from 0.6 to 0.9 times the whole width W0 of the rubber tape, and an opening thickness HA1 of from 1.5 to 7.5 times the average thickness of the central part of the rubber tape,
the calendar rollers provided therebetween with a gap between which the extruded rubber passes through, the gap having a shape which is similar to but smaller than a cross sectional shape of the rubber tape.